/*
 * efone - Distributed internet phone system.
 *
 * (c) 1999,2000 Krzysztof Dabrowski
 * (c) 1999,2000 ElysiuM deeZine
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 */

/* based on implementation by Finn Yannick Jacobs */

#include <stdio.h>
#include <stdlib.h>
#ifndef __sun__
#include <stdint.h>
#else
#define uint32_t unsigned int
#endif

#define u_int32_t uint32_t

/* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
 *		so make sure, you call it before using the other
 *		functions!
 */
u_int32_t crc_tab[256];

/* chksum_crc() -- to a given block, this one calculates the
 *				crc32-checksum until the length is
 *				reached. the crc32-checksum will be
 *				the result.
 */
u_int32_t
chksum_crc32 (char *bloc, unsigned int length)
{
  register unsigned long crc;
  unsigned long i;
  unsigned char *block = (unsigned char *) bloc;

  crc = 0xFFFFFFFF;
  for (i = 0; i < length; i++)
    {
      crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
    }
  return (crc ^ 0xFFFFFFFF);
}

/* chksum_crc32gentab() --      to a global crc_tab[256], this one will
 *				calculate the crcTable for crc32-checksums.
 *				it is generated to the polynom [..]
 */

void
chksum_crc32gentab ()
{
  unsigned long crc, poly;
  int i, j;

  poly = 0xEDB88320L;
  for (i = 0; i < 256; i++)
    {
      crc = i;
      for (j = 8; j > 0; j--)
	{
	  if (crc & 1)
	    {
	      crc = (crc >> 1) ^ poly;
	    }
	  else
	    {
	      crc >>= 1;
	    }
	}
      crc_tab[i] = crc;
    }
}
